The present invention generally relates to a copying arrangement and more particularly, to a copying apparatus for effecting copying operations by subjecting an original document scanning means including a reciprocating means such as an optical unit, original document platform or the like, to a constant speed scanning.
More specifically, the present invention relates to a copying apparatus provided with an original document scanning means including a reciprocating means such as an optical unit or original document platform, etc., with the scanning speed thereof being adapted to be controlled according to the copying magnifications, and characterized in that an acceleration time required for the original document scanning means to scan from its home position, for example, to an original document leading edge position is obtained by information acquired in advance through a preliminary scanning, and timing for feeding copy paper sheets is arranged to be determined based on a reference time obtained by adding to said acceleration time, time required for an exposure position on a photoreceptor drum to reach a transfer position, and time required for feeding the copy paper sheet between a copy paper sheet leading edge position and an image leading edge position in the case where copying is effected at a central portion of a copy paper sheet.
Conventionally, for copying images of an original document onto a copy paper sheet, there has been employed a practice to effect the copying at a position where the original document is slightly deviated with respect to the copy paper sheet depending on necessity. However, the known practice as referred to above is such that, with respect to a reference time point when an original document scanning means has reached the position of the original document leading edge, timing for feeding the copy paper sheet is determined within the range in which the original document scanning means is moved at a constant speed, and thus, the shiftable distance thereby is limited only to approximately several tens of millimeters.
Referring to FIG. 3, there is shown a schematic diagram for explaining a general construction and functions of an optical system movable type copying apparatus, which generally includes a housng H, an original document platform 7 of a transparent material such as a glass plate or the like, provided at the upper portion of the housing H, an optical unit including a first mirror 1, a second mirror 2 and a third mirror 3 and also a zoom lens 5 and a fourth mirror 4 and disposed below and adjacent to the platform 7, a photoreceptor drum 6 having a photosensitive surface 6a on its outer peripheral portion and rotatably provided generally at the central portion of the housing H, and a copy paper sheet feeding passage G having a paper start clutch PSC at a position P6 and provided at the lower portion of said housing H for feeding the copy paper sheets accommodated in a paper sheet cassette F towards the transfer position at P5 immediately below the photoreceptor drum 6.
In the copying apparatus of FIG. 3, scanning of an original document (not shown) placed on the platform 7 is effected as the optical unit including the first, second and third mirrors 1, 2 and 3 scans said platform 7. The copy paper sheet fed along the feeding passage G is once stopped at the position P6 for the paper start clutch PSC so as to be further transported at a predetermined timing. In the arrangement as described so far, it has been a conventional practice that a timer (not shown) is actuated from a time point when the first mirror 1 has reached a point P2 so as to control the paper start clutch PSC after a lapse of a predetermined period of time, and in this case, a maximum shiftable distance may be represented by L1-L2 when a distance between the exposure position P4 and the transfer position P5 of the photoreceptor drum 6 is denoted by L1 and a distance between the position P6 for the clutch PSC and the transfer position P5 is represented by L2. Therefore, the shiftable distance is limited only to 10 to 20 mm at the most as described earlier. Meanwhile, when the original document scanning means is arranged to travel at a constant speed before the leading edge of the original document is subjected to exposure, the distance to be covered from the starting of the original document scanning means to the exposing of the original document leading edge must be set to be large, thus resulting in a large size of the copying apparatus on the whole.
However, it has been a recent trend that copying magnifications applicable to actual copying tend to expand in directions both for enlargement and contraction, while image editing is also extensively effected, with large shifts e.g. in the order of 100 and 200 mm which can not be achieved by the conventional image shifting methods coming to be required. Therefore, for example, transfer of a contracted image onto the central portion of a copy paper sheet (referred to as "centering" hereinafter) could not be effected automatically.